Process for generating gases and apparatus therefor



June 1963 A. c. SCURLOCK ETAL 3,092,958

PROCESS FOR GENERATING GASES AND APPARATUS THEREFOR 6 Sheets-Sheet lOriginal Filed Nov. 6, 1957 June 1963 A. c. SCURLOCK ETAL. 3,092,963

PROCESS FOR GENERATING GASES AND APPARATUS THEREFOR 6 Sheets-Sheet 2Original Filed Nov. 6, 1957 June 1963 A. c. SCURLOCK ETAL 3,

PROCESS FOR GENERATING GASES AND APPARATUS THEREFOR 6 Sheets-Sheet 3Original Filed Nov. 6, 1957 III I I II! &

INVENTORS Amy C 5604 1 OC'K,

J1me 1963 A. c. SCURLOCK ETAL 3,

PROCESS FOR GENERATING GASES AND APPARATUS THEREFOR 6 Sheets-Sheet 4Original Filed Nov. 6, 1957 Wig u U INVENTRS ARM 6 Sea/e1 0m,

June 1963 A. c. SCURLOCK' ETAL 3,092,968

PROCESS FOR GENERATING GASES AND APPARATUS THEREFOR 6 Sheets-Sheet 5Original Filed Nov. 6, 1957 IVENTORE d/FC'H 5 560m 00%,

June 11, 1963 A. c. SCURLOCK ETAL 3,092,968

PROCESS FOR GENERATING GASES AND APPARATUS THEREFOR Original Filed Nov.6, 1957 6 Sheets-Sheet 6 INVENTORS Aem 6 5209mm,

United States masses Patented dune ll, 19%3 nice 3,992,968 PROCESS FQRGENERATTNG GASES APJD APPARATUS TEEREFQR Arch C. Scnrlock, Arlington,Keith E. Rumbel, Falls Church, and Raymond Friedman, Alexandria, Va.,assignors to Atlantic Research fiorporation, Alexandria, Va, acorporation of Virginia Original application Nov. 6, 1957, Ser. No.694,894. Di-

vided and this application Dec. 17, 1959, Ser. No. 860,291

12 Claims. (Cl. 6039.47)

This invention relates to a new process for generating gases bycombustion of a plastic, extrudable monopropellant for such purposes asproducing thrust, power, heat energy or gas pressure and apparatustherefor. This is a divisional application of Arch C. Scurlock et al.application, Serial No. 694,894, filed November 6, 1957.

The term monopropellant refers to a composition which is substantiallyself-sufficient with regard to its oxidant requirements as distinguishedfrom bipropellants Where the fuel is maintained separately from theoxidizer source until admixture at the point of combustion.

Generation of gases for producing thrust, as in a jet motor, or as aprime mover, as in a gas turbine, has hitherto generally beenaccomplished either by burning atomized sprays of mobile liquid monoorbipropellant injected from a storage tank or tanks into the combustionchamber or by combustion of a solid propellent grain housed in thecombustion chamber. Although each of these methods possesses desirableadvantages relative to the other, each is also characterized byundesirable features.

The use of mobile liquid monopropellants, namely propellants which areinjectable into a combustion chamber in the form of finely divideddroplets or sprays, has the following important advantages. The massburning rate and, thereby, the volume of combustion gases produced arecontrollable by varying the rate of injection. Cornbustion can bestopped by shutting ofi flow and resumed at will. Performance is notdependent upon the temperature environment of the system. Duration ofoperation is limited only by capacity of the storage tanks orreservoirs. Liquid monopropellants, furthermore, possess an importantadvantage over liquid bipropellants since the former require only onestorage tank, one pr-opellent pump, and one set of feed lines andvalves, and eliminate elaborate systems for ensuring properlyproportionated flow of the separate fuel and oxidizer components andtheir adequate admixture in the combustion chamber.

However, the usual mobile liquid monopropellants are characterized bydisadvantages such as low density, low specific impulse, high toxicity,excessive sensitivity to heat and shock resulting in detonation, andcorrosiveness to various parts of the system, such as valves. When usedin a rocket motor, there is some tendency for unburned droplets of theliquid propellant to leave the combustion chamber and to be cooledduring expansion in the nozzle before combustion occurs. Performance mayalso be affected by attitude of the system.

Not only is a complex system of tubing, valves, and usually pumpsrequired to fill the liquid propellent tanks and to move the propellantfrom there into the combustion chamber, but provision must be made topurge the system of propellant after test firings are made. Metalcatalysis problems are sometimes encountered in passing the liquidthrough the complex system. Catalyst beds are required for combustion ofsome liquid monopropellants and vibration of the system often posesproblems of retaining the bed firmly fixed in the combustion chamber.Storage and transportation of liquid propellants is also a problembecause of their tendency to leak readily. Such leakage presents both afire and toxicity hazard.

Solid propellants, as a means for generating gases, possess theadvantages of high density, low heat and shock sensitivity, goodstability, long storageability, absence of leakage, low corrosivenessand toxicity and elimination of propellent filling and injectionequipment and controls since all of the solid propellant is containeddirectly in the combustion chamber. Solid propellants do not requirepurging of the system after test firing, do not need an externalcombustion catalyst and are not affected by the attitude of the system.

Such gas generating, solid propellent systems do, however, possess anumber of disadvantages. The solid grain must be sufficiently strong andfree from mechanical flaws so that it does not crack or shatter underpressure or vibrational stresses. Many solid propellants also tend tobecome excessively brittle at low ambient temperatures and therebysubject to fracture. Cracking or shattering of the propellent grain inthe combustion chamber may cause such a large, uncontrolled increase inburning surface that the walls of the combustion chamber cannotwithstand the pressure. Although a burning solid propellent grain can bequenched, if necessary, by suitable means, reignition is not feasible,so that the unburned portion is a total loss and intermittency ofoperation is impractical. Ambient temperature of the propellent grain isan important parameter in determining burning rate and cannot becompensated for during use by variation of the area of burning surface.

Solid propellent grains must be predesigned and preshaped with respectto burning surface area for each particular application, since such areais set for a given grain and cannot subsequently be varied. This makesnecessary the production and storage of a large variety of grains ofdifferent design. pellent grains cannot accommodate during burning tovariations in operational requirements or to difierent ambienttemperatures. The only way in which a solid propellent gas-generatingcomposition can be designed to meet unforeseen operational requirementsis to produce an adequate supply of gases at the extremes of high usagerequirements and low ambient temperature, which in most casesnecessitates venting and wasting surplus gas at other operatingconditions. Wastage in this manner can be as high as of the gas producedand provides a design problem in terms of a modulating valve which canwithstand the high temperature exhaust gases. Size of the grains mustalso be predetermined and permits no subsequent variation in amountconsumed unless Waste of an unburned portion of the grain poses noeconomic or other problem. Maximum duration of burning time or thrust isconsiderably shorter than that which can be provided by a liquidpropellant which is limited largely by storage capacity of thereservoir.

The combustion chamber must be of sutiicient size to accommodate all ofthe propellant and, therefore, is generally larger than required forcombustion of a liquid propellant. Since the walls of the entirecombustion chamber must be strong enough to withstand the highcombustion gas pressures and completely insulated or otherwise cooled toWithstand the high combustion gas temperatures, this may pose a moreserious weight problem than that of a pnopellent storage tank. Thegeometry of the combustion chamber is, furthermore, immobilized by thedesign requirements of the propellent grain and cannot, in many cases,be adapted to the particular structural needs of the device as a whole.

The general object of this invention is to provide a new method forgenerating gases employing a plastic monopropellant which combines mostof the advantages Such predesigned solid proof methods employing eithermobile liquid propellants or solid propellants and which eliminates mostof their disadvantages.

Another object is to provide a new method for generating gases whichmakes possible controlled feeding of a monopropellant into a combustionchamber, a controllable burning surface not dependent upon subdivisionor atomization in the combustion chamber, reduced combustion chambersize, quenching and reignition and tolerance of system attitude, andwhich, furthermore, makes possible the use, in the foregoing manner, ofcompositions characterized by high density, high impulse, highautoignition temperature, non-leakage and substantial freedom from shocksensitivity, corrosiveness and toxicity.

Still another object is to provide a new method for generating gaseswhich makes possible the use, in the aforedescribed manner, ofmonopropellant compositions which can be safely prepared, handled andstored.

Another object is to provide a new method for generating gases havinghigh available energy for developing thrust or power as, for example,for use in jet or rocket reaction motors, gas turbines, reciprocatingengines and the like or for providing heat or gas pressure.

A futher object of the invention is the provision of ap paratus forimplementing the method in the fulfillment of the foregoing objects, andother objects which will appear as the following description proceeds.

In the drawings:

FIGURE 1 is a longitudinal cross-sectional view through a diagrammaticembodiment of the invention.

FIGURE 2 is a cross-sectional view along line 22 of FIGURE 1 showing theextruder plate and mass flow control and cut-01f device in partiallyclosed position.

FIGURE 3 is a fragmentary cross-sectional view taken on line 33 ofFIGURE 2.

FIGURE 4 is similar to FIGURE 2 but showing the device in closedposition.

FIGURES 5 and 6 are fragmentary perspective views of the equilibriumburning surface of a strip of extruding monopropellant at differentrates of extrusion.

FIGURE 7 is a cross-sectional view similar to FIGURE 2 showing amodified extruding plate and mass flow control and cut-off deviceadapted for use in a cylindrical chamber in open position.

FIGURE 8 shows the device of FIGURE 7 in closed position.

FIGURES 9 and 10 are fragmentary perspective views showing theequilibrium cone-shaped burning surface formed by a column of extrudingmonopropellant in the combustion chamber at different rates ofextrusion.

FIGURE 11 is a vertical sectional view of a modified form of the device.

FIGURE 12 is a horizontal sectional view'taken along the line 1212 ofFIGURE 11.

. FIGURE 13 is a view similar to FIGURE 12 but showing the device inclosed position.

FIGURES 14 and 15 are fragmentary sectional views of the equilibriumburning surface of the extruding monopropellant at different rates ofextrusion.

FIGURE 16 is a plan view showing another modification of the propellantshaping means.

FIGURE 17 is a vertical sectional view taken along the line 1717 ofFIGURE 16.

FIGURES 18 and 19 are fragmentary sectional views of two differentflow-dividers.

FIGURE 20 is a fragmentary plan view of another gridtype shaping means.

FIGURE 21 is a plan view showing concentric flowdividers.

FIGURE 22 is a vertical sectional view taken along line 22-22 of FIGURE21.

FIGURE 23a is a fragmentary vertical sectional view showing amandrel-type flow-divider and extruding propellant prior to ignition.

FIGURE 23b is similar to FIGURE 23a showing the equilibrium burningsurface.

FIGURE 24 is a schematic perspective view of 4 different mandrel-typeflow-dividers.

FIGURE 25 is a planview of still another form of flowd-ivider shapingmeans.

FIGURE 26 is a vertical cross-sectional view taken along line 2626 ofFIGURE 25.

FIGURE 27 is a plan view of still another modified flow-divider shapingmeans.

FIGURE 28 is a vertical cross-sectional View taken along line 28--28 ofFIGURE 27.

We have discovered a new and highly advantageous method for generatinggases which comprises extruding a plastic monopropellant composition,having sufiicient cohesive strength to retain a formed shape and capableof continuous flow at ordinary to reduced temperatures under pressure,from a storage chamber into a combustion chamber in the form of anydesired coherent shape, such as a column, strip, or the like and burningthe leading face of the continuously advancing material in thecombustion chamber. The leading face of the shaperetaining mass thuspresents a burning surface of predeterminable area which can be variedand controlled by varying the rate of extrusion, and/ or varying thesize and shape of the cross-sectional area of the feeding or extrusionorifices or tubes and/ or by shaping or recessing the leading face ofthe advancing mass to increase the available burning surface by suitablemeans. The extent of overall burning surface area can also be regulatedby providing a plurality of feeding orifices or tubes which can bevaried in number. Thus, mass burning rate of the monopropellant and theamount and pressure of combustion gases generated can easily beregulated by controlled feeding.

In this way, the rate of gas generation can be tailored to particularrequirements both before and during operation within limits set by theparticular properties of the monopropellant compositions and thestructural limitations of the rocket, gas generator or other device.Similarly, factors affecting burning rate of the propellant material,such as its ambient temperature or pressure conditions in the combustionchamber, can be compensated for by controlling feeding rate oradjustment of the size or shape of the mass of extruded propellant.

Because of the fluidity of the material under stress at ambienttemperatures, the monopropellant can be fed into the combustion chamberat a rate adjusted to the desired mass burning rate of the compositionso that at equilibrium or steady-state burning, namely when the massburning rate does not vary with time, the burning surface of thecontinuously extruding propellant remains substantially stationaryrelative to the Walls of the combustion chamber. Since burning isconfined to a welldefined burning surface area, much as in the case ofthe burning of solid propellant grains, combustion chamber lengthrequirements are generally quite small, both as compared with thatneeded for complete reaction of sprayed or atomized conventional mobileliquid propellants and for housing of conventional solid propellentgrains. This makes possible a substantial saving in dead weight, sincethe combustion chamber not only must be built to withstand the highcombustion gas pressures, but must also be heavily insulated and made ofmaterials, generally heavy, such as alloy steels or nickel alloys, suchas Inconel, which are resistant to the corrosive gases. Unlike solidpropellent combustion chambers, which must conform to designrequirements of the propellent grain, the combustion chamber employed inour process can be designed to meet the shape or other requirements ofthe particular gas generator device.

Duration of combustion is limited only by the capacity of themonopropellent storage container and appropriate means for cooling thewalls of the combustion chamber, where necessary, and can be continuousor intermittent. Combustion can be quenched at any time by any suitablemeans, such as a cut-off device which shuts 01f further propellentextrusion into the combustion space and can be placed in any appropriateposition relative to the extrusion orifice, and can be reinitiated byopening the shut-ofi mechanism and reigniting the leading face of theextruding propellant. In some applications, intermittency of operationis not necessary and a cut-off mechanism can be dispensed with, althoughit may be desirable in such a situation to seal off the propellant inthe storage chamber from the combustion chamber by means which can beopened or ruptured when operation begins.

Another advantage of our invention stems from the substantialnon-fluidity of the monopropellants except under stress since, unlikemobile liquids it makes the system substantially immune to attitude.This makes unnecessary elaborate precautions to maintain the storedpropellant during operation in constant communication with a pumpingmeans or the feeding orifice into the combustion chamber.

Controllable feeding of the monopropellant eliminates the wastageencountered with solid propellants by premitting regulation both beforeand during operation to meet environmental factors and varyingoperational needs and the necessity for manufacturing and storing alarge variety of solid propellent grains predesigned with regard toburning surface area characteristics and size.

Like conventional mobile liquid monopropellants, as distinguished fromliquid bipropellants, the system requires only one storage container orreservoir and one set of pressuring means, feeding tubes and controlvalves, thereby simplifying the complexity of the device and reducingweight. There is also no need for combustion catalysts in the combustionchamber.

In operation, the plastic monopropellant is extruded from the storagechamber through a shaping means such as a tube or orifice of anysuitable size, shape and number, into the combustion chamber by means ofany suitable pressurizing device, such as a piston or bladder actuatedby a pressurized fluid or a properly designed pump, which can exert asufficiently high positive pressure on the monopropellant relative tothat in the combustion chamber to keep the propellant flowing into thecombustion chamber at a linear rate at least equal to the linear burningrate of the propellent composition and at such higher rates as might berequired to obtain desired variation in mass burning rate and gasproduction. The shaping means, such as a tube or orifice, which can befurther provided with means for shaping or recessing the leading end ofthe material to increase available burning surface area, functionssubstantially as a die forming the extruding material into a cohesive,shape-retaining advancing mass, such as a column or strip, ofpredetermined shape and of predetermined cross-sectional area, which canbe varied by providing means for reducing or increasing thecross-sectional area of the orifice either before or during operation.

The leading face of the extruding column or strip of propellant can beignited in the combustion chamber by any suitable means, such as anelectrical squib, high resistance wire, electric arfc or spark gap. Theburning leading face thereby provides a constantly generating burningsurface, predetermined in size and geometry by the size and shape of theextrusion shaping means, such as a tube or orifice, by any shaping orreoessing means associated with the tube or orifice, and by the rate ofextrusion, as the end-burning material advances. As aforementioned, theminimum rate of extrusion of the monopropellant must be at least equalto the linear burning rate of the composition and preferably higher toprevent burning back into the propellent storage chamber.

Prior to ignition, the leading face of the extruding propellent masswill generally approximate a plane surface, as shown in FIGURE 1. Afterignition, if extrusion rate is about equal to linear burning rate of thecomposition, burning of the extruding material takes place substantiallyat the point of entry into the combustion chamber, for

example, at the orifice, and the burning surface, which is, in effect,the leading face of the propellent material, retains the form of atransverse plane. At the preferred higher rates of extrusion, a longercolumn or strip projects into the combustion chamber and, under theinfiuence of the circulating high-temperature combustion gases, burningextends upstream along the exposed surface of the extruding mass withinthe combustion chamber. When burning equilibrium is reached at a givenrate of extrusion which is higher than linear burning rate, the surfaceof the propellent material protruding into the combustion chamberconverges in the downstream direction, forming a downstream edge whenthe material is extruded as a strip or ribbon, as illustrated in FIGURES5, 6, 14, 15, 16, and 2.1, or a downstream apex when the material isextruded through a circular orifice as illustrated in FIG- URES 9 and10, or a rectangular orifice as shown in FIG- URE 20, thereby providinga convergent leading face or end and a burning surface of desiredextensive area.

The burning sunface area of such sloping configurations is determined bythe angle subtended by the converging sides, which is determined -by thelength of the propellent strip or column protruding into the combustionchamber from the downstream edge or apex to the orifice, which, in turn,is determined largely by the rate of extrusion. The higher the rate ofextrusion, the longer is the column or strip, the more acute is theangle sub-tended by the sloping sides, and the greater is the burningsurface, as shown in FIGURES 6, 10 and 15. Thus the burning surfacearea, which, in turn, determines the mass burning rate and the mass rateof gas generation, can be controlled by vaiying the rate of extrusion ofthe monopropellant. It will be seen, therefore, that controlled feedingand, thereby, controlled rate of gas generation can be achieved 'byvarying the rate of extrusion. This can be readily accomplished bycontrolling extrusion pressure on the propellant with the aid ofsuitable regulatory devices.

Feeding and mass burning surface area can also be varied and controlledby providing suitable shaping means as the propellant mass is extrudedfrom the storage chamber into t e combustion chamber. The propellant canbe divided into a plurality of substantially separate extruding shapedmasses of substantially any desired size or configuration, such ascolumns or strips of any desired crosssectional shape, into a pluralityof substantially separate shaped masses, some or all of which have theirleading faces shaped, as, for example by recessing, to increase burningsurface area or formed into a single advancing mass having its leadingface shaped by suitable recessing means to provide a desired increase inburning surface area, relative to the length of the extruding mass.

The propellent shaping means can be any suitable device foraccomplishing the desired shaping or shaping and dividing of anextruding propellant. It can, for example, be an extrusion plate of anydesired and suitable strength and depth, provided with a plurality oforifices of any desired and suitable shape and size spaced at asubstantial distance from each other, as illustrated in FIGURES 1, 7,11, 23a, and 27, or it can be reduced to a plurality of flow dividers ofrelatively small width and depth spaced and positioned relative -to eachother in any suitable manner and configuration for a given application,as illustrated in FIGURES 16, 20 and 21.

An extrusion plate having orifices which are substantially spaced fromeach other possesses certain advantages such as making possibleincreased strength to withstand high extrusion pressures, variation insize of the individual orifices before or during operation, asillustrated in FIGURES 2 and 3, and internal cooling of the platesurface exposed to the hot combustion gases in the combustion chamber,as illustrated in FIGURE 28, by interior circulation of a cooling fiuid.

Reducing the space between orifices to yield flow-dividers of narrowwidth, on the other hand, permits con siderable reduction in weight andmakes possible extrusion of increased amount of propellant by maximizingtotal 7 cross-sectional area of the orifices as illustrated in FIG- URES16, 20, and 21. Shortening the depth of the flow dividers reducesfrictional resistance to flow and the pressure differential required tomaintain extrusion at the desired rate. A flow divider of small mass canalso more readily be kept cooled by flow of the mass of unburnedpropellant past it than can a flow separator having a relatively largesurface exposed to the combustion chamber.

In some cases the advantages of orifices substantially spaced from eachother and narrow flow dividers can be combined by introducing into theformer a narrow divider, such as a wire, as shown in FIGURES ll, 12 and13. The narrow flow divider can be one or several and can be positionedin the larger orifice in any desired manner or configuration.

- An important advantage of flow dividers of small cross sectional area,such as wires, lies in the fact that they can be employed as igniters,as shown diagrammatically in FIGURE 12, both initially to ignite thepropellent material and to reignite it for intermittent operation.

A given extruding mass of the plastic monopropell-ant, such as a columnor strip of the material, can also have its leading face shaped orrecessed to increase burning surface area by means of a flow divider, soassociated with the extrusion tube or orifice and of such dimensionsthat it is completely within the peripheral boundary of flow of theextruding propellant. Such a flow divider, which will hereinafter betermed a mandrel, produces an axial recess or bore in the leading faceof the monopropellant as the latter is extruded around it and therebyexposes additional propellent surface. The shape and cross-sectionalarea of the recess is determined by the configuration and size of themandrel, which can be varied as desired. A spherical mandrel, forexample, produces a cylindrical bore in the unignit-ed material, asshown in FIGURE 23a. When the propellant is ignited, this interiorlyexposed surface becomes part of the burning surface and, at burningequilibrium, slopes to a leading edge to form, in the case of acylindrical bore, an inverted cone within the leading face of theextruding propellant, as shown in FIGURE 2312, thereby considerablyincreasing burning surface area. The cone angle and depth are determinedby the rate of extrusion; the higher the rate, the more acute is theangle and the deeper the cone.

Other suggested shapes of mandrel are indicated in FIG- URE 24 in whichthe reference characters A and D refer respectively to a cone and cube,which produce respectively a cylindrical and rectangular bore throughthe extrusion. The reference characters B and C refer to elongatedbodies forming bores of oblong cross section, that produced by mandrel Cbeing a narrow slot.

The mandrel can be positioned just above the extrusion orifice, justwithin the extrusion orifice, as illustrated in FIGURES 23a and 23b, ordown inside an extrusion tube, as illustrated in FIGURE 28. In thelatter case burning takes place within the extrusion tube on theinterior, inverted conical surface of the extruding mass and the portionof the tube above the burning surface becomes part of the combustionchamber. Burning within a tube, which can be of any desiredcross-sectionalshape, has the advahtage both of permitting internalcooling of the walls, as illustrated in FIGURE 28, and of supporting theperiphery of the extruding mass. Such a peripheral support may beadvantageous when the device is subjected to severe accelerativestresses .to prevent fragmentation of the material. The mandrel in thiscase produces the desired large burning surface area.

The'combustion chamber itself can be employed as a single extrusion tubeof large cross-sectional area with the leading face of the extrudingmonopropellant shaped into a burning surface of large total area bymeans of plurality of mandrels, each of which forms a recessed burningarea, as illustrated, for example, in FIGURES 25 and 26. The shape ofsuch an extruding burning surface can be varied as desired by varyingthe number, size and shape of the mandrels.

Decreasing the cross-sectional area of an extrusion orificeproportionately decreases the cross-sectional area of the shaped mass ofmaterial extruding at a given linear rate of extrusion and, thereby,reduces the amount of burning surface area at equilibrium burning.Increasing the size of the orifice has the opposite effect. In the caseof an orifice which is substantially longer than it is wide in itstransverse dimensions relative to the axis of propellant flow, adecrease in its longer dimension, so long as length remains greater thanwidth, does not change the height of the burning extruding propellantmass at the given linear rate of extrusion at equilibrium burning.

If, however, the orifice is reduced in its smaller transverse dimensionas, for example, the Width of a slot orifice, height of the extrudingburning mass at a given linear extrusion rate is reduced, and totalburning surface area is reduced in amount proportional to the reductionin orifice area. In the case of a symmetrical orifice, such as acircular orifice, any reduction in cross-sectional area reduces heightof the burning extruding mass at a given linear rate of extrusion. Byheight of the extruding mass is meant the linear distance from itsleading edge or apex to the extruding orifice.

Thus it may require two or more narrow orifices to provide the sametotal burning surface area as would a single wide orifice but thenarrower orifices provide the advantages, important in someapplications, of permitting use of a shorter combustion chamber, or ofsubstantially increasing the upper limit of extrusion rate. The higherthe extrusion rate, the greater is the height of the extruding column orstrip. Maximum practical height is determined in some applications bythe cohesiveness of the propellant composition, namely the distance towhich it can be extruded without sagging under the stress of its ownweight, and in other cases by accelerative or vibrational stresses whichmight cause fragmentation of excessively long extruded masses. Similarresults are obtained by decreasing the size and increasing the number ofsymmetrical orifices or by more closely spacing a plurality of mandrelsin a mass of extruding propellant. Narrow flow-dividers as shown inFIGURES l2, 16, 20, and 21 possess the advantage of maximizing thenumber of narrow orifices possible as well as maximizing totalcross-sectional area of the orifices.

The generated high-energy gases can be used to produce thrust as, forexample, in the rocket motor of a plane, projectile, or jet-assisttake-01f unit, or for prime rnovers such as in a gas turbine,reciprocating engine, or the like. They can be employed to drivetorpedoes, helicopters, fluid and jet pumps, auxiliary power supplyunits and the like.

FIGURE 1 shows diagrammatically a rocket motor device employing our newprocess for generating gases. The monopropellant 1, which is a plastic,cohesive, shaperetaining composition capable of continuous flow undersmall to moderate pressure, is contained in storage chamber 2. Tank 3contains a gas, such as air, under high pressure which feeds into pistonchamber 4 via valve regulator 5 and pipe 13 and actuates piston 6,thereby exerting pressure on the propellant, causing it to flow andextrude in the form of strips or ribbons 7 through rectangular slotorifices 8 in a suitably insulated plate 9 separating the propellentstorage chamber from combustion chamber 10 provided with a suitablelayer of insulation 11.

A valve regulator system maintains a positive pressure in piston chamber4 relative to combustion chamber pressure which is sufliciently high tomaintain propellent extrusion at the desired extrusion rate, which is atleast as high as the linear burning rate of the propellant andpreferably higher. A suitable system for this purpose is showndiagrammatically. Regulator 5 contains a cylindrical bore 38 providedwith annular grooves 21 and 22 forming annular gas ports which can becompletely or partially opened or completely closed by longitudinalmotion of cylindrical valves 23 and 24, connected by rod so that theymove simultaneously. Tank 3 is connected by pipe 26 with po t 21 throughwhich it feeds pressurized gas into pipe 13 and piston chamber 4 in anamount determined by the position of valve 23. When port 21 is open,port 22 is closed. When valve 23 moves to the right sutficiently toclose port 21, valve 24 also moves to open port 22 and some pressurizinggas in the piston chamber 4 vents through pipe 13, port 22 and exhaustpipe 27 opening out of port 22, thereby reducing the pressure on themonopropellant and its extrusion rate when necessary. Motion of valves23- and 24 and, thereby, pressure in the piston chamber 4 and extrusionrate, is controlled by pressure-responsive regulator 23 which istransversely partitioned by diaphragm 29 into two chambers 30 and 31.Tube 12 communicates to chamber 30 the combustion gas pressure in thecombustion chamber. Chamber 31 is maintained at a predetermined pressurelevel by means of tube 32 connected to pressurized gas tank 3 and aregulatory solenoid valve 33. Coil springs 34 and 35 act as restoringforces on the diaphragm to reduce reaction time lag. Motion of thediaphragm is communicated to valves 23 and 24 by connecting rod 36.Bellows 37 serves as a gas seal.

The regulatory system functions as follows. Pressure in chamber 31 isset at the desired level of combustion chamber pressure which in turn isproduced by burning of the propellant at a particular, required rate ofpropellant extrusion. This can readily be calculated from knowledge ofthe burning characteristics of the particular propellent composition, inthe total burning surface area presented by the extruding propellant asdetermined by the cross-sectional area of the extruding orifices andother known factors such as the size and shape of the combustion chamberand the Venturi nozzle. So long as this desired combustion chamberpressure is maintained, diaphnagm 29 is in neutral position andpressurizing gas is fed through port 21 into the piston chamber in therequired amounts to maintain the requisite rate of extrusion. Ifcombustion chamber pressure drops, the diaphragm is pushed to the left,valve 23 moves to the left, more pressurizing gas is fed into the pistonchamber, extrusion rate increases, mass burning rate increases, andcombustion chamber pressure is increased to the desired level. Ifcombustion chamber pressure rises beyond the desired level, thediaphragm moves to the right, port 21 closes, exhaust port 22 opens andsufiicient gases vent from the piston chamber to reduce extrusion rateto the requisite degree.

The system can be further controlled to regulate and vary the rate ofextrusion to meet variations in operating requirements during theburning cycle by means of solenoid valves 33 and 34, which can bepreprogrammed or voluntarily controlled to increase or decrease theregulating pressure in chamber 31. Valve 34 and exhaust tube 35 permitventing of gas from chamber 31 when a reduction in extrusion rate isdesired.

Transversely slidable plate 15 is provided with rectangular slotorifices 16 which are similar in size, shape, and spacing to orifices 8in extruder plate 9 so that in a given position of plate 15, orifices 16and 8 are in registry and both open to their fullest extent as shown.The slidable plate orifices are each provided with a shearing edge 14.Transverse slidable motion of the plate is produced by motor 17 whichcan be remote-controlled. Undesirable lateral motion of plate 15 ischecked by pin and slot guide 20 and 20a. The propellant extruded intothe combustion chamber is not burning, as shown, but ignition can beaccomplished by resistance wire igniter 18 of which there may be morethan one. The high pressure gases generated after burning is initiatedvent through rocket nozzle 19 at high velocity to produce thrust.

Slidable plate 15 can be used to reduce mass flow of the propellant bybeing moved into a position across extrusion orifices 8, as shown inFIGURES 2 and 3 wherein it reduces their eifective size, or it can beemployed as a cut-off device completely to stop flow by covering theentire extrusion orifice, as shown in FIGURE 4.

FIGURES 5 and 6 show the downstream sloping or substantially V-shapeconfiguration of the burning surface or leading face 7a of the extrudingstrip of monopropellant of FIGURE 1 in the combustion chamber whenequilibrium or steady-state burning has been reached at different ratesof extrusion. The rate of extrusion in FIG- URE 6 is higher than inFIGURE 5 so that height of the extruded portion of the strip is greater,the sides of the V-shaped face slope more steeply, and burning surfacearea 7b is greater.

FIGURES 7 and 8 show a modification in which extrusion plate "40 isprovided with circular extrusion orifices 41 and transversely slidablemass flow control and cut-off plate 42 is provided with similarly spacedorifices 43 having a shear edge 44, which in FIGURE 7 are shown incompletely open registry with extrusion orifices 41 in the extrusionplate 40. In FIGURE 8, the cut-01f plate has been moved so thatextrusion orifices 41 are completely covered and flow of propellant isstopped.

FIGURES 9 and 10 show the cone-shaped equilibrium burning surfaces 45and 45a formed by the leading face of propellant extruding through acircular orifice, such as shown in FIGURE 7, at different rates ofextrusion, that of FIGURE 10 being higher and, therefore, providinggreater burning surface area.

FIGURE 11 is substantially similar to the device of FIGURE 1 with thefollowing modifications. Extrusion plate 51 is provided with slotorifices 52, each of which has a longitudinal flow-divider 53 in theform of a wire. The wire flow-divider in effect divides the largerorifices 52 into narrower orifices. Cut-off plate 54 provided withorifices 55, shown in registry with orifices 52 in FIGURES 11, 12, 14and 15 and having shear edge 56, is positioned beneath the extrusionplate and can be shifted laterally by motor 17 to cut off flow ofmonopropellant through orifices 52 as shown in FIGURE 13. Guide pins 57and slots 58 hold the cut-off plate in position against the extrusionplate and prevent undesirable sidewise motion. The flow dividers 53 arehigh resistance wires which can be employed as igniters by connectingthem by means of properly insulated wires 59 to a source of electriccurrent, as shown diagrammatically in FIGURES 12 and 13. Prior toignition the monopropellant extrudes in pairs of substantiallyplane-surfaced narrow strips or ribbons as shown in cross-section inFIGURE 11. After ignition, when equilibrium burning is reached, theburning surfaces 61 and 62 assume the downstream-convergentconfigurations shown in FIGURES l4 and 15. The rate of extrusion ishigher in FIGURE 15, thereby resulting in anextruded strip of increasedheight.

FIGURES 16 and 17 show a modified shaping means for the monopropellantextruding from the propellent reservoir 2 which comprises a plurality ofparallel wire flow dividers with a cut-off plate omitted. FIGURE 17shows, in cross section, the equilibrium burning surface 71 of theextruded strips or ribbons of monopropellant.

FIGURES 18 and 19 illustrates respectively flow dividers of differentconfiguration, flow-divider 72 being V- shaped and flow-divider 73 beingtriangular prismatic.

FIGURE 20 illustrates another grid-type flow-divider shaping means inwhich crossing narrow flow-dividers 74 and 75 form rectangular orifices76. The extruding propellant at equilibrium burning assumes the leadingface configuration substantially as shown with four substantially planesides converging into a leading apex.

FIGURE 21 illustrates concentric flow-dividers in the form of rings 80,which, as shown, are shallow but which can be of any desired depth. Therings are held in position by vertical rods 81 attached to the side wallof the chamber by spider 82. The extruding monopropel- 1 l lant isshaped by the rings into concentric annular ribbons or strips 83 and acentral column 84. At burning equilibrium the leading face of theextruding propellant assumes the sloping configuration as shown inFIGURES 21 and 22, strips 83 having an annular leading edge 85 and thecentral column having leading apex 86.

FIGURES 23a and 23b illustrate the shaping and recessing effect of aspherical mandrel 87 positioned at the mouth of extrusion orifice 88 inextrusion plate 89. The mandrel is anchored by means of rod 90 andspider 91. The mandrel shapes a recess 92 in the leading face 93 of theextruding propellant which is a cylindrical bore as shown in FIGURE 23aprior to ignition and provides additional exposed surface. Atequilibrium burning the burning surface slopes downstream as shown inFIGURE 23b to form an annular conical face 94 having a central conicalrecess 95.

FIGURE 24 illustrates diagrammatically some diiferently shaped mandrels.which can be used as flow dividers.

FIGURES and 26 illustrate the use of a plurality of spherical mandrels100 to shape the leading face of a single mass of extruding propellantwith the walls of the combustion chamber 101 forming in effect a largeextrusion tube. The propellant is extruded from storage chamber 102. Atequilibrium burning as shown, the surface exposed by the mandrels as thepropellant is extruded past them burns into the shape of recessed cones103 which flare downstream and intersect with each other to form curvedridges 104 and apical points 105. The mandrels are anchored in positionby rods 106 and spider .107.

FIGURES 27 and 28 show a plurality of extrusion tubes 110 in hollowplate or partition 111 which provides a chamber for circulation ofcoolant around the extrusion tubes as shown. The propellant .1 isextruded from storage chamber 112 into extrusion tubes 110 where itflows past spherical mandrels 113 positioned within the tubes at a pointsubstantially below their downstream ends. The leading face of thepropellent mass extruding within each tube is recessed by the mandrel113. Burning takes place within the tube and at equilibrium the burningsurface assumes the shape of an inverted cone 114, as shown, with theouter periphery of the mass supported by the Walls of the extrusiontube. The portion of each tube downstream of the burning surface formspart of the combustion chamber 115. The mandrels are held in position byrods 116 and spider 117.

In some special applications, as, for example, where the monopropellantis a heterogeneous system comprising a dispersion of solid oxidizer in asubstantially inert liquid fuel so that an inhibiting layer of theliquid fuel may form on the periphery of the advancing column or stripof monopropellant as a result of shearing stresses at the wall duringextrusion and where the combustion chamber is so designed as to minimizehot combustion gas circulation or is swept by relatively cool gases,such as steam, the burning surface may not extend upstream along thesides and will maintain substantially the transverse plane configurationof the unignited propellant shown in FIG- URE 1. In such case controlledfeeding and burning surface area can be achieved by varying the size,shape and number of the extruding orifices.

As aforementioned, the monopropellant should possess certain requisitephysical characteristics. It should be sufficiently cohesive to retainits shape for an appreciable length of time when extruded. Preferablyalso, its cohesive strength should be suificiently high to withstandfragmentation under the given conditions in the combustion chamber. Thisis of importance not only for control of the desired burning surfacearea, but to avoid loss or wastage of unburned propellant in someapplications, as )for example, rocket motors, by venting of the materialout of the nozzle under such conditions as high acceleration. This isfrequently a problem in the case of the burning of atomized mobileliquid propellants, some unburned particles of which fly out of therocket nozzle. The degree of cohesive strength desirable is determinedto some extent by the particular stresses developed in a particular useand the particular burning conditions as, for example, the unsupportedlength of the extruding, burning mass. Cohesive strength is closelyrelated to the tensile strength of the material. In general, for thedesired shape-retentivity, the monopropellant material should preferablyhave a minimum tensile strength of about 0.01 lb./sq. in., preferablyabout 0.03 p.s.i. or higher.

The cohesiveness or substantial tensile strength of the monopropellantmaintains stability and uniform dispersion of its components as, forexample, in the case of two-phase systems containing dispersedinsoluble, solid oxidizer. This is of considerable importance, since itensures uniformity of burning rate at the constantly generating burningsurface as the end-burning material advances, thereby assuring aconstant or controllable rate of gas generation.

The monopropellant, furthermore, should be extrudable at ambienttemperatures, namely, should be capable of continuous flow, preferablyunder relatively moderate pressure differentials. Materials which areextrudable only at elevated temperatures or which require excessivelyhigh pressures to initiate and maintain flow present problems which makethem generally unsuitable. In general, it is desirable to employ amaterial which flows at a maximum shear stress of about '1 p.s.i. at thewall of the tube or orifice through which it is being extruded. In someapplications, the shear stress point can be higher, as, for example, upto about 10 p.s.i. or more, where stronger pressurizing means forextrusion are feasible.

The controllable feeding of a monopropellant having bothshape-'retentiveness and fluidity under stress substantially eliminatesstill another difiiculty encountered with solid propellants housed inthe combustion chamber, namely, the dangers of fracturing or cracking ofthe solid propellant which can so enormously increase burning surfacearea and the amount of gases produced as to cause explosion of thecombustion chamber. The brittleness and fissuring characteristic of manysolid propellants at low ambient temperatures is no problem withmonopropellants having the physical characteristics requisite for ourpurpose since they can either be formulated so as to have exceedinglylow freezing points or, upon warming to ambient temperatures of use,regain their flow characteristics and form a continuous, unbroken massduring pressure extrusion.

Substantially any monopropellent composition having the requisitephysical characteristics, as for example, gelled liquid monopropellantssuch as hydrazine nitrate, nitromethane, or ethylene oxide containing asuitable gelling agent can be employed. One of the important advantagesof the invention, however, stems from the fact that the process makespossible the utilization of propellent compositions possessing thehighly desirable characteristics of solid propellants in terms, forexample, of the high density and high impulse required for highperformance levels and reduced storage volume requirements with theimportant concomitant advantages of propellent feed control and,thereby, control of gas gen.- eration under varying circumstances.

Double base propellent compositions comprising nitrocellulosegelatinized with nitroglycerin with or without, but preferably with, aninert, nonvolatile plasticizer such as triacetin, diethyl phthalate,dibutyl phthalate or dibutyl sebacate, to reduce impact sensitivity, inproportions producing a soft gel having the requisite shaperetentiveness and flow characteristics are suitable for use. Suchrelatively high-density, high-impulse propellants have hitherto beenutilizable only as solid propellants with the predesigning, presizingand other disadvantages entailed by this mode of use.

In general, gel compositions comprising about 3 to 25 nitrocellulosedissolved in nitroglycerin, desirably diluted with at least aboutpreferably at least 20 to 30% by weight based on total liquid, of aninert plasticizer solvent to reduce sensitivity, possess the requisitephysical properties. Such soft gel compositions also have the advantageof being admixable with finely divided insoluble solid oxidizer such asthe ammonium, sodium, and potassium perchlorates and nitrates, toprovide for combustion of the inert plasticizer, while retaining thedesired shape-retentive, extrudable characteristics. Other highly activepropellent liquids, such as pentaerythritol trinitrate,1,2,4-butanetriol trinitrate, and diethylene-glycol dinitrate, whichnormally are too sensitive for use as mobile liquid monopropellants, canalso be gelatinized With nitrocellulose, with or without inertplasticizer diluent and with or without finely divided solid, insolubleoxidizer, to provide monopropellants of substantially higher densitythan presently usable mobile liquid monopropellants.

Still another advantage of the process lies in the fact that it makespossible combustion with controllable feeding and gas generation ratesof heterogeneous monopropellants which are characterized not only byhigh density and high impulse, but also by the high autoignitiontemperature, low shock-and-impact sensitivity, non-corrosiveness andnontoxicity of many of the presently used solid composite-typepropellants, which make them safe to handle, to transport and to storefor extended periods of time under substantially any environmentaltemperature conditions likely to be encountered. By heterogeneous ismeant a two-phase system wherein a finely divided, solid oxidizer isdispersed in an organic liquid fuel in which the oxidizer is insoluble.Spraying or atomization into a combustion chamber of dispersions of asolid oxidizer in a liquid fuel, even where the solid is present insutficiently small amounts so that the slurry is free-flowing, is notfeasible. The solid tends to clog the small atomization orifices.Oomminution of the composition into a finely divided spray in thecombustion chamber also poses reaction problems because of thedifiiculty in maintaining the solid oxidizer phase and the liquid fuelphase in properly proportioned contact for complete oxidation.

Heterogeneous monopropellent compositions which are particularlyadvantageous comprise stable dispersions of finely divided, insolublesolid oxidizer in a continuous matrix of a nonvolatile, substantiallyshock-insensitive liquid fuel, the composition having sufficiently highcohesive strength to form a plastic mass which maintains the solidom'dizer in stable, uniform dispersion and which, while capable ofcontinuous flow at ambient temperatures under stress, neverthelessretains a formed shape for an appreciable length of time. Thecompositions, which preferably are soft gels, possess thecharacteristics of non- Newtonian liquids, namely yield to flow onlyunder a finite stress.

The liquid fuel can be any oxidizable liquid which is preferably highboiling and substantially nonvolatile, which is preferably free-flowingor mobile at ordinary temperatures, desirably having a maximumsolidification or pour-point of about 2 C. or less, and which issubstantially inert or insensitive to shock or impact. The lattercharacteristic can be achieved by employing an oxidizable liquid, atleast about 50% by weight of which is an inert compound requiring anexternal oxidizer for combustion. For special applications, an activeliquid fuel containing combined oxygen available for combustion of othercomponents of the molecule, such as nitroglycerin, diethylene glycoldinitrate, pentaerythritol trinitrate or 1,2,4-butane-triol trinitrate,can be admixed with the inert fuel component, such dilution servingsubstantially to nullify the sensitivity of the active component.

The inent liquid fuel is preferably an organic liquid which, in additionto carbon and hydrogen, can contain other elements such as oxygen,nitrogen, sulfur, phosphorus or silicon and which-meets theaforedescribed requirements in terms of physical and chemicalproperties. Such liquid fuels burn to produce gaseous combustionproducts and include hydrocarbons, e.g., triethyl benzene, dodecane andthe like; compounds containing some oxygen linked to a carbon atom, suchas esters, e.g., methyl maleate, diethyl phthalate, butyl oxalate,dibutyl sebacate, dio'otyl adipate, etc.; alcohols, e.g., benzylalcohol, diethylene glycol, triethylene glycol, etc.; ethers, e.g.,methyl o-naph-thyl ether; ketones, e.g., benzyl methyl ketone, phenylo-tolyl ketone, isophorone; acids, e.g., 2-ethylhexoic acid, oaproicacid, n-heptylic acid, etc.; aldehydes, e.g., cinnemaldehyde;nitrogen-containing organic compounds such as amines, e.g.,N-ethylphenylamine, tri-nbutylamine, diethyl aniline; nitnles, e.g.,caprinitrile; phosphorus-containing compounds, e.g., triethyl phosphate;sulfur-containing compounds, e.g., diethyl sulfate; pentamethyldisiloxanemethyl methacrylate, and many others.

The solid oxidizer can be any suitable, active oxidizing agent whichyields oxygen readily for combustion of the fuel and which is insolublein the liquid fuel vehicle. Suitable oxidizers include the inorganicoxidizing salts, such as ammonium, sodium, potassium and lithiumperchlorate or nitrate, and metal peroxides such as barium peroxide. Thesolid oxidizer should be finely divided, preferably with a maximumparticle size of about 300 to 600 microns, to ensure stable, uniformdispersion of the oxidizer in the liquid fuel so that it will notseparate or sediment despite lengthy storage periods, although somesomewhat larger particles can be maintained in gelled compositionswithout separation.

The amount of liquid fuel vehicle in the composition is critical onlyinsofar as an adequate amount must be present to provide 'a continuousmatrix in which the solid phase is dispersed. This -Will vary to someextent with the particular solids dispersed, their shape and degree ofsubdivision and can readily be determined by routine rtest formulation.The minimum amount of liquid required generally is about 8%, usuallyabout 10%, by weight. Beyond the requisite minimum any desiredproportion of liquid fuel to dispersed solid can be employed, dependingon the desired combustionproperties, since the desired cohesive,shape-retentive properties can be obtained by additives such as gellingagents. Where the requisite cohesiveness and plasticity are obtained byproper size distribution of the finely divided solid, without anadditional gelling agent, the amount of solid incorporated should besufii-cient to provide the consistency essential for shape-retentiveness. This will vary with the particular liquid vehicle,the particular solid and its size distribution and can readily bedetermined by routine testmg.

Thixotropic, plastic, shape-retentive compositions having the desirableflow characteristics can be made by incorponating sufiicient finelydivided solid, insoluble oxidizer into the liquid fuel to make anextrudable mass when particles are so distributed that the minimum ratioof size of the largest to the smallest particles is about 2:1 andpreferably about 10:1. At least of the particles by weight shouldpreferably have a maximum size of about 300 microns. Above this, a smallproportion by weight up to about 600 microns can be tolerated.

-It is generally preferable to incorporate a gelling agent in the solidoxidizer-liquid fuel dispersion. Such gels possess the desireddispersion stability, cohesiveness, shaperetentiveness and flowcharacteristics. Any gelling agent which forms a gel with the particularliquid fuel can be employed. Examples of compatible gelling agentsinclude natural and synthetic polymers such as polyvinyl chloride;polyvinyl acetate; cellulose esters, e.g., cellulose acetate andcellulose acetate butyra-te; celluose ethers, e.g., ethy cellulose and'carboxymethyl cellulose, metal salts of higher fatty acids such as theNa, Mg and Al stearates, palrnitates and the like; salts of naphthenicacid, casein; hanaya gum; gelatin; bentonite clays and amine- '15treated bentonite clays; etc. Organic gelling 'agents are preferredsince they can also serve as fuels. The amount of gelling agent employedis largely determined by the particular liquid fuel, the particulargelling agent, the amount of dispersed solid, and the specific physicalproperties desired.

Particle size distribution of the dispersed solids is generally not animportant factor in imparting cohesive, plastic properties to thecomposition and in minimizing separation where a gelling agent isemployed since these factors are adequately provided for by the gel.Even some substantially l'arge solid particles as, for example, up toabout 1000 microns, can be held in stable dispersion. However, thepresence of different size particles is often desirable because of theimproved packing etfect obtained, in terms of increased amounts ofsolids which -can be incorporated.

Finely divided, solid metal powders, such as Al or Mg, can beincorporated in the monopropellant compositions as an additional fuelcomponent along with the liquid fuel. Such metal powders possess theadvantages both of increasing density and improving specific impulse of.the monopropellant because of their high heats of combustion. The metalparticles should preferably be within a size range of 0.25 to 50microns. The amount of such metal fuel added is not critical but isdetermined largely by the specific use and the requisite physicalcharacteristics of the composition as aforedescribed. For example, itshould not be incorporated in such large amounts that the mixture eitherbecomes granular in texture or deficient in amount of oxidizer. Ingeneral the maximum amount of metal powder which can be introduced whilemaintaining the desired physical properties (of the composition and anadequate amount of solid oxi- (dizer is about 45% by Weight, and dependsupon the density of the metal and its chemical valence or oxidant:requirement for combustion.

stoichiometric oxidizer levels [with respect to the liquid fuel orliquid plus powdered metal fuels 'are sometimes desirable forapplications where maximum heat release is "wanted. Actualstoichiometric amounts of oxidizer vary, of course, with the particularfuel components and the particular oxidizer and can readily be computedby any one skilled in the art. {in general, however. the amount requiredwill be in substantially major proportion as, for example, about 65% andgenerally more, of the total composition. The requisite highconcentrations of solid oxidizer for stoichiometry can generally bereadily incorporated, particularly where the liquid fuel contains :somecombined oxygen as aforedescri-bed, while maintaining its essentialphysical characteristics.

In some cases, as, for example, where the monopropellant is beingemployed in a gas generator for driving ;a turbine, reciprocatingengine, or the like, as a source of gas} pressure, or to provide heatenergy, the amount :of oxidizer can be less than stoichiometric so longas nuificient is introduced to maintain active combustion :and a desiredlevel of gas generation. The presence of an active liquid fuelcomponent, namely a fuel containing oxygen available for combustion,reduces, of course, the amount of solid oxidizer required both forstoichiometric and less-than-stoichiometric combustion levels.

Example I 74.2% ammonium perchlorate (a mixture of 1725 r.p.m. and14,000 r.p.m. grinds in a ratio of 1:2, 4-400 microns, 98% by weightunder 300 microns), 24.8% triacetin and 1% copper chromite were admixedat room temperature. The resulting composition was a cohesive,shape-retentive mass which could be made to flow continuously undermoderate pressure. The composition had an autoignition temperature of275 C. and an impact sensitivity of 80/85 cm. with a 3.2 kg. weight.Burning rate of the material at atmospheric pressure was 0.04

in./sec. The material was extruded through a stainless 16 steel tube0.162 in. in diameter into a nitrogen-filled chamber and the leadingface burned at a rate of 0.1 in./sec. at 35 p.s.i.

Example II A gel was made with ammonium perchlorate (1725 and 14,000r.p.m. grinds, 1:2) 25% dibutyl sebacate and 1% polyvinyl chloride. Thepolyvinyl chloride was mixed with the dibutyl sebacate and heated to 172C. to form a gel, which was cooled and loaded 'with the ammoniumperchlorate. The composition was a plastic, shape-retentive mass havinga tensile strength of 0.31 p.s.i. Length of an extruded column beforebreak ing under its own weight was 5 inches. Shear stress at the wallrequired to initiate flow in a V8 in. diameter tube was 0.035 p.s.i.

The dispersion was highly stable as shown by vibrator tests at 60 cyclesand an acceleration of 4 g. No separation occurred after hours. Thematerial was also tested by centrifuge at an acceleration of 800 g. andshowed no separation after 30 minutes.

Autoignition temperature of the composition Was 286 C. and itssolidification or freezing point 18C.

The composition extruded as a shaped mass through a 12 in. tube with0.375 in. bore at a rate of 0.25 in./sec. under a pressure of 11p.s.i.g.

Linear burning rate of the material at 70 F. and 1000 p.s.i. was 0.46in./sec.

Although this invention has been described with reference toillustrative embodiments thereof, it will be apparent to those skilledin the art that the principles of this invention may be embodied inother forms but within the scope of the appended claims.

We claim:

1. A gas generating apparatus comprising means forming a storagechamber, a plastic, shape-retentive monopropellant contained thereinwhich is extrudible under pressure at ambient temperature, saidmonopropellant being an ignitible composition which is self-sufiicientin its oxident requirements and which burns to produce hot combustiongases, means forming a combustion chamber, partition means having anorifice therethrough separating said storage chamber and said combustionchamber, means for progressively extruding a continuous mass of saidmonopropellant from said storage chamber through said orifice into saidcombustion chamber at a rate at least as high as the linear burning rateof the monopropellant, said mass being laterally shaped by said orifice,and a relatively narrow flow-divider bridging said orifice forprogressively recessing the leading face of the laterally-shaped massextruding through said orifice, and means for igniting said extruded,shaped mass in the combustion chamber.

2. A gas generating apparatus for using a plastic, shaperetaining,extrudible monopropellant comprising means forming a storage chamber forsaid monopropellant, means forming a combustion chamber, means forprogressively extruding a continuous mass of said monopropellant intosaid combustion chamber at a rate at least as high as the linear burningrate of the monopropellant, mandrel means positioned to shape the lead-7 ing face of said mass as it advances into said combustion chamber, andmeans for igniting said extruded, shaped mass in the combustion chamber.

3. A gas generating apparatus for using a plastic, shaperetaining,extrudible monopropellant comprising means forming a storage chamber forsaid monopropellant, means forming a combustion chamber, means forprogressively extruding a continuous mass of said monopropellant intosaid combustion chamber at a rate at least as high as the linear burningrate of the monopropellant, partition means separating said storage andcombustion chambers, an orifice opening therethrough for laterallyshaping said mass as it advances into said combustion chamber, a mandrelspaced from the boundary 17 Wall of said orifice located in the normalgeometrical projection of said orifice for progressively displacing suchportion of said shaped mass as it contiguously confronts, and means forigniting said extruded, shaped mass in the combustion chamber.

4. A gas generating apparatus for using a plastic, shaperetaining,extrudible monopropellant comprising a housing, a flow divider in theform of a closed loop intermediately positioned within said housing, thepart of said housing beneath the plane of said flow divider being astorage'chamber for the monopropellant, the part of said housing abovesaid flow divider being a combustion cham her, said flow divider beingspaced from said housing in said plane, means for extruding themonopropellant from said storage chamber into said combustion chamber ata rate at least as high as the linear burning rate of themonopropellant, said flow divider displacing the part of the mass thatit contiguously confronts, thereby recessing the mass in said combustionchamber, and means for igniting said extruded, shaped mass in thecombustion chamber.

5. A gas generating apparatus for handling a plastic, shape-retaining,cohesive extrudible monopropellant, comprising a housing, intermediatelypositioned parallel tubes Within said housing and arranged in a bundle,a mandrel in each tube, that part of said housing above the plane ofsaid mandrels, including the space within said tubes, being a combustionchamber, that part of said housing below said plane, including the spacewithin said tubes, being a storage chamber for the monopropellant, thatpart of said housing in the zone of said tube bundle and outside saidtubes being a chamber for a coolant, means for extruding monopropellantfrom said storage chamber through said tubes to said combustion chamberat a rate at least as high as the linear burning rate of the monopropellant, said mandrels being in the path of flow of the extrudingmass of monopropellant, said mandrels displacing the part of the massthat they contiguously confront, thereby recessing said mass in saidcombustion chamber, and means for igniting said extruded, shaped mass inthe combustion chamber.

6. A gas generating apparatus for handling a plastic, shape-retainingextruding monopropellant, comprising a housing, intermediately andaxially positioned parallel tubes within said housing, a mandrel in eachtube, that part of said housing above the plane of said mandrels,including the space said tubes, being a combustion chamber, that part ofsaid housing below said plane, including the space within said tubes,being a storage chamber for the monopropellant, means for extrudingmonopropellant from said storage chamber through said tubes to saidcombustion chamber at a rate at least as high as the linear burning rateof the monopropellant, said mandrels being in the path of flow of theextruding mass of monopropellant, said mandrels displacing the part ofthe mass that they contiguously confront, thereby recessing said mass insaid combustion chamber, and means for igniting said extruded, shapedmass in the combustion chamber.

7. A gas regenerating apparatus which comprises housing means defining acombustion chamber and a storage chamber, a plastic, shaperetaining,extrudible monopropellant contained within said storage chamber, saidmonopropellant being an ignitible composition which is selfsufiioient inits oxidant requirements and which burns to produce hot combustiongases, orifice means separating said chambers, means for extruding acontinuous mass of the monopro-pellant from said storage chamber throughsaid orifice means into said combustion chamber at a rate at least ashigh as the burning rate of the monopropellant, said orifice meansserving laterally to shape said extruding mass, means positioned in thenormal geometrical projection of said orifice means for recessivelycontouring the leading face of the laterally shaped extruding mass, andmeans for igniting said extruded, shaped mass in the combustion chamber.

8. The gas generating apparatus of claim 1 which includes a cut-offplate contiguous to said partition means and slidable relative theretoand having an aperture therethrough movable with said cut-ofi plate intoand out of registry with said orifice in said partition means.

9. The gas generating apparatus of claim 1 in which said partition meansforms a chamber providing for circulation of coolant around saidorifice.

10.. The gas generating apparatus of claim 3 which includes a cut-offplate contiguous to said partition means and slidable relative theretoand having an aperture therethrough movable with said out-oflf plateinto and out of registry with said orifice in said partition means.

'11. The gas generating apparatus of claim 3 in which said partitionmeans forms a chamber providing for circulation of coolant around saidorifice.

12. The gas generating apparatus of claim 7 in which said orifice meansforms a chamber providing for circulation of coolant.

References Cited in the file of this patent UNITED STATES PATENTS515,500 Nobel Feb. 27, 1894 2,510,572 Goddard June 6, 1950 2,523,012Goddard Sept. 19, 1950 2,810,259 Burdett Oct. 22, 1957 2,971,097 CorbettFeb. 7, 196 1 FOREIGN PATENTS 582,621 Great Britain Nov. 22, 1946

1. A GAS GENERATING APPARATUS COMPRISING MEANS FORMING A STORAGECHAMBER, A PLASTIC, SHAPE-RETENTIVE MONOPROPELLANT CONTAINED THEREINWHICH IS EXTRUDIBLE UNDER PRESSURE AT AMBIENT TEMPERAATURE, THENONOPROPELLANT BEING AN IGNITIBLE COMPOSITION WHICH IS SELF-SUFFICIENTIN ITS OXIDENT REQUIREMENTS AND WHICH BURNS TO PRODUCE HOT COMBUSTIONGASES, MEANS FORMING A COMBUSTION CHAMBER, PARTITION MEANS HAVING ANORFICE THERETHROUGH SEPARATING SAID STORAGE CHAMBER AND SAID COMBUSTIONCHAMBER, MEANS FOR PROGRESSIVELY EXTRUDING A CONTINUOUS MASS OF SAIDMONOPROPELLANT FROM SAID STORAGE CHAMBER THROUGH SAID ORIFICE INTO SAIDCOMBUSTION CHAMBER AT A RATE AT LEAST AS HIGH AS THE LINEAR BURNING RATEOF THE MONOPROPELLANT, SAID MASS BEING LATERSLLY SHAPED BY SAID ORIFICE,SAID A RELATIVELY NARROW FLOW-DIVIDER BRIDGING SAID ORIFICE, FORPROGRESSIVELY RECESSING THE LEADING FACE OF THE LATERALLY-SHAPED MASSEXTRUDING THROUGH SAID ORIFICE, AND MEANS FOR IGNITING SAID EXTRUDED,SHAPED MASS IN THE COMBUSTION CHAMBER.